The invention relates to supercharging systems associated with internal combustion engines in motor vehicles.
Supercharging systems make it possible to increase the quantity of air admitted into the engine. Supercharging systems comprise a turbocompressor formed of a turbine and of a compressor coupled to the turbine. An electronic control unit which controls the general operation of the engine makes it possible to control the supercharging system.
The turbine is disposed at the exit of the exhaust manifold and is driven by the exhaust gases.
The compressor is disposed upstream of the engine air intake manifold and is able to compress the air admitted by the engine. The compressor is driven by the turbine.
In the case of a supercharging system comprising a fixed-geometry turbocompressor (FGT), the power provided to the turbine by the exhaust gases can be modulated by means of a discharge valve able to tap off a part of the exhaust gases at the turbine inlet. In the case of a supercharging system comprising a variable-geometry turbocompressor (VGT), the power provided to the turbine by the exhaust gases can be modulated by means of adjustable vanes at the turbine inlet.
For this purpose, an actuator controlled by the electronic control unit makes it possible to drive the opening and closing of the valve or vanes of the turbocompressor.
Currently, the requirements in terms of responsiveness of diesel engines lead to the imposition on supercharging systems of constraints demanding very short response times. It follows that the electronic control unit is programmed to drive the turbocompressor at operating points approaching the operating limits of the turbocompressor.
In particular, under certain conditions, when the driver of the vehicle lifts his foot abruptly from the accelerator pedal, a pumping phenomenon occurs which manifests itself through large oscillations of the air flow rate into the intake manifold of the engine. This pumping phenomenon is prejudicial to the operation of the engine and can cause deterioration in the turbocompressor. Furthermore, this pumping phenomenon is unpleasant for the driver (appearance of air noise, loss of engine power).
Document DE 101 54 151 A1 describes a method for limiting the pumping phenomenon during a phase of sudden dip in injection. The method comprises a step consisting in detecting a variation in the acceleration command and a step consisting in, as a function of this variation, maintaining the variable-geometry turbocompressor in a maximum opening configuration.
This method does not enable the pressure at the outlet of the compressor to be made to drop as rapidly as possible nor does it make it possible to maintain the air flow rate into the intake since it is limited by the engine speed.
Furthermore, the effectiveness of this method depends on the setting of the parameters for regulating the regulated operating mode.